Polymerization flow focusing

Early work on the use of optical methods on the dynamics of polymeric liquids focused on establishing the validity of the stress-optical rule. A comprehensive account of this research can be found in the books by Janeschitz-Kriegl [29] and Wales [84], The majority of studies have considered simple shear flow, and the rule has been found to hold up to... 

We have recently reported [60] a DOD system in a stiff polymeric device based on an integrated microvalve [54]. This system allows for formation of both droplets and bubbles on demand (Fig. 9), in both the flow-focusing and the T-junctions, and can be made compatible with any chemistry by the virtue of its compatibility with both polymeric and glass devices. 

Bon and Kumacheva and coworkers [104] demonstrated that monodisperse solids-stabilized droplets could be generated in a microfluidic flow focusing device, whereby the solid particles were initially present in the dispersed phase. Polymerization of the monomer droplets led to hybrid polymer microspheres. They also showed that non-spherical particles could be obtained by geometric confinement of the droplets in the channel [104,105]. 

The very first flow focusing device was developed by Stone and coworkers [11] and was used for the emulsification of water in silicone oil. The geometry of this device is depicted in Figure 18.7 and was obtained after replication of a positive relief of the microchannels patterned in SU-8 photoresist. The authors named this FFD a microfluidic flow focusing device (MFFD). A few years after the development of this microsystem, Kumacheva and coworkers [12] used an MFFD (Figure 18.7, top left) made out of PDMS or polyurethane (PU) for the emulsification and polymerization of several multifunctional acrylates ethylene glycol dimethacrylate (EGDMA),... 

Abraham et al. [48] fabricated spherical polymeric microcapsules by flow focusing of an organic phase consisting of amphiphilic block copolymer solution in DCM vhth a continuous aqueous phase in a cross-junction microchannel of 100 x 100 pm channel cross-section. The ratio of the flows of the two immiscible solutions... 

Microdevices may also be very effective and have also been proposed for nanoparticle production even if the flow is laminar, the very small size of the chaimel can allow very intensive mixing, but caution has to be taken because the small channels can be easily plugged [60,62]. However, two systems have been proposed and tested for particle precipitation one is based on the collision of microfragments [63], the other uses flow focusing in microfluidic channels to control nanoprecipitation of poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) diblock copolymer as a model polymeric biomaterial for drug delivery [64]. 

Figure 8.12a-c illustrates the constituent components and an M reactor comprised of eight MF modules, used for the continuous synthesis of polymer poly(N-isopropylacrylamide) microspheres [82]. The particles were produced by MF emulsification of the aqueous solution of the monomer N-isopropylacrylamide mixed with a photoinitiator and subsequent photoinitiated polymerization of the monomer to form microgel particles. Each individual reactor contained an emulsification compartment and the polymerization compartment (Figure 8.12a). The emulsification of the solution of N-isopropylacrylamide was carried out in a flow-focusing droplet generator.

Rhee M, Valencia PM, Rodriguez MI, Langer R, Farokhzad OC, Kamik R (2011) Synthesis of size-tunable polymeric nanoparticles enabled by 3D hydrodynamic flow focusing in single-layer microchannels. Adv Mater 23(12) H79-H83... 

Polymeric fluids are the most studied of all complex fluids. Their rich rheological behavior is deservedly the topic of numerous books and is much too vast a subject to be covered in detail here. We must therefore limit ourselves to an overview. The interested reader can obtain more thorough presentations in the following references a book by Ferry (1980), which concentrates on the linear viscoelasticity of polymeric fluids, a pair of books by Bird et al. (1987a,b), which cover polymer constitutive equations, molecular models, and elementary fluid mechanics, books by Tanner (1985), by Dealy and Wissbrun (1990), and by Baird and Dimitris (1995), which emphasize kinematics and polymer processing flows, a book by Macosko (1994) focusing on measurement methods and a book by Larson (1988) on polymer constitutive equations. Parts of this present chapter are condensed versions of material from Larson (1988). The static properties of flexible polymer molecules are discussed in Section 2.2.3 their chemistry is described in Flory (1953). 

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